1. Field of the Invention
The present invention relates to a nozzle gap adjusting method for setting a predetermined small gap, without contact, between a working fluid ejection nozzle and a workpiece in a wire electric discharge machine.
2. Description of the Related Art
In a wire electric discharge machine (wire EDM), a wire electrode is fed in an axial direction thereof while moving a workpiece and the wire electrode relatively to each other in a direction substantially perpendicular to the axial direction of the wire electrode. In the process, working fluid is ejected from a nozzle toward the machined portion, and intermittent voltage pulses (or voltage pulses constituting discharge pulses) are applied between the wire electrode and the workpiece so that the electric discharge is generated to machine the workpiece.
In this wire EDM, the positioning and adjustment of the upper nozzle is performed to set a predetermined gap between the upper nozzle and the workpiece. Especially, the upper nozzle gap is required to be set properly in order to prevent the wear of the nozzle and to achieve a normal machining accuracy and normal machining rate.
In the prior art, the operator sets the upper nozzle gap by inserting a gap gauge between the upper nozzle and the workpiece and moving a Z-axis moving member along the Z-axis while checking the gap size, setting the Z-axis moving member in position to secure the desired upper nozzle gap. In this way, all the jobs for nozzle gap adjustment are carried out manually and, therefore, the problem is posed that such an adjustment consumes much time on the one hand and the result of adjustment is undesirably varied on the other hand.
Specifically, in order to prevent the nozzle wear and maintain a stable machining rate and machining accuracy, it is desirable to maintain a predetermined small gap between the forward end of the nozzle and the workpiece during the machining. However, no conventional method is available whereby the gap can be set both rapidly and accurately. In order to obviate this situation, Japanese Patent No. 2576050 proposes a nozzle apparatus in which a forward end of a nozzle is brought into contact with a surface of a workpiece and then separated from the workpiece surface by a predetermined distance thereby to secure a predetermined distance between the nozzle forward end and the workpiece surface.
However, in the nozzle apparatus disclosed in the above-described patent, since the forward end of the nozzle is brought into contact with the workpiece and the nozzle position setting is performed with reference to a contact point between the forward end of the nozzle and the workpiece, a problem is encountered that the machine may be damaged by the contact with the workpiece.